Both Uses

coup
in
The Hunt for Red October
(Auto-generated)

It would be the intelligence coup of all time.†
Chpt 6. *
As a practical matter, having the officers is as great a coup as having the submarine.†
Chpt 8.

Definitions:

(1) (coup as in: deposed in the coup)
the sudden overthrow of a government by use of limited force

This sense of coup is also called a coup d'état.
(2) (coup as in: a financial coup)
a brilliant and notable success

The term "coup de theatre" indicates a sensational moment in a theatrical stagecraft -- typically a surprise; or possibly a highly successful theatrical production.
(3) (coup de grace as in: delivered the coup de grace)
deathblow

(literally a sword strike that mercifully kills a wounded animal, or metaphorically as the last in a series of things that defeated an opponent, idea, business or other entity.)

The term coup de grace indicates a merciful death blow.
(4) (meaning too rare to warrant focus)